1. Field of the Invention
The present invention relates to a valve manifold for controlling fluid flow between a main flowline and a plurality of pressure sensors/transmitters.
2. Description of the Prior Art
It is frequently necessary to obtain pressure and/or flow characteristics of a fluid in a pipeline or flowline. One common way to accomplish this is by disposing in the flowline a restriction such as an orifice plate, a flow nozzle, or a venturi tube. The high and low pressure values taken from opposed sides of the flow restriction in the flowline are detected by a pressure sensor/transmitter assembly that measures and/or transmits the measured pressures or pressure differential by a suitable mechanical or electrical signal to a remote location, e.g., a control room.
Typically, a valve manifold is mounted between the flowline and the pressure sensor/transmitter, the manifold, in addition to controlling flow to the pressure sensor/transmitter, permitting various functions such as blocking, venting, zero checking, and calibration. A typical manifold includes a plurality of valves, each movable between open and closed positions relative to a flow pathway in the manifold so as to control the flow of fluid through the pathway.
There is an ever increasing desire by the manufacturers of pressure sensors/transmitters to reduce the size, not only of the pressure sensor/transmitter, but also of the package comprised of the manifold that attaches to the flowline and the attached pressure sensor/transmitter. Large, heavy manifold/pressure transmitter packages are more expensive to make, difficult to handle and install, and in many cases simply will not fit appropriately in their intended environment, meaning they have to be installed at another location or in undesirable orientations.
In co-pending application Ser. No. 08/941,951, filed Oct. 1, 1997, and entitled Two-Piece Manifold, there is disclosed a two-piece modular manifold comprised basically of what may be characterized as a process module and an instrument module, the process module being connected to the flowline, the instrument module mating with the pressure sensor/transmitter. The modular manifold disclosed in the latter mentioned patent application is extremely compact and is especially useful for a single, coplanar pressure sensor/transmitter and, more specifically, a differential pressure sensor/transmitter.
It is frequently desired not only to have a differential pressure measurement across the flow restrictor in the pipeline, but also to be able to determine absolute line pressure. For the latter purpose, a gauge pressure transmitter is installed on the pipeline, the gauge pressure transmitter measuring the pressure upstream of the flow restrictor in the flowline. In the distant past, this generally required a separate installation for the differential pressure transmitter and the gauge pressure transmitter. This was clearly undesirable as it increased the likelihood of leakage since it required two separate taps in the flowline installations. Moreover, the requirement of two installations mandated the use of a larger amount of space, often times in environments where space was at a premium. To overcome the problem of two separate installations, various solutions have been proposed. For example, in U.S. Pat. No. 5,036,884, the problem of overcoming dual installations was addressed by means of a valve manifold and an interfacing or transmitting mounting plate providing communication between the valve manifold and the two different transmitters. However, this solution required that the two main block valves that control flow from the high and low pressure outlets from the main flowline, plus any equalizing or venting valves, be carried by the manifold. Furthermore, the assembly shown in U.S. Pat. No. 5,036,884 is bulky and subject to undesirable torsional and bending loads, particularly in flowlines subject to vibrations and/or pulsations from compressors, pumps, and the like in the flowline. To overcome these torsional and bending loads, it is desirable to reduce, to the extent possible, the distance between the orifice taps in the flowline and the laterally outwardmost portions of the manifold/pressure sensor unit package.